Highly sensitive and selective analysis of urinary steroids by comprehensive two-dimensional gas chromatography combined with positive chemical ionization quadrupole mass spectrometry

Comprehensive two dimensional gas chromatography (GC × GC) provides greater separation space than conventional GC. Because of fast peak elution, a time of flight mass spectrometer (TOFMS) is the usual structure-specific detector of choice. The quantitative capabilities of a novel GC × GC fast quadrupole MS were investigated with electron ionization (EI), and CH 4 or NH 3 positive chemical ionization (PCI) for analysis of endogenous urinary steroids targeted in anti-doping tests. Average precisions for steroid quantitative analysis from replicate urine extractions were 6% (RSD) for EI and 8% for PCI-NH 3 . The average limits of detection (LODs) calculated by quantification ions for 12 target steroids spiked into steroid-free urine matrix (SFUM) were 2.6 ng mL −1 for EI, 1.3 ng mL −1 for PCI-CH 4 , and 0.3 ng mL −1 for PCI-NH 3 , all in mass scanning mode. The measured limits of quantification (LOQs) with full mass scan GC × GC-qMS were comparable with the LOQ values measured by one-dimensional GC-MS in selected ion monitoring (SIM) mode. PCI-NH 3 yields fewer fragments and greater (pseudo)molecular ion abundances than EI or PCI-CH 4 . These data show that a benchtop GC × GC-qMS system has the sensitivity, specificity, and resolution to analyze urinary steroids at normal urine concentrations, and that PCI-NH 3 , not currently available on most GC × GC-TOFMS instruments, is of particular value for generation of structure-specific ions. GC × GC-qMS was evaluated for urinary steroid ( i.e. testosterone/epitestosterone) analysis using electron ionization (EI) and positive chemical ionization with NH 3 (PCI-NH 3 ).